Several designs of microfluidic valves exist for various microfluidic applications, such as single purpose, multipurpose, or general purpose Lab on Chip (LoC), microfluidic crystallization devices, sorting devices, arrayers, etc. Generally these devices provide an arrangement of channels defined between two meeting surfaces, such as formed within a layered microfluidic device.
To selectively close or open passages in such devices, it is known to use pneumatically controlled polymer valves obtained by multilayer soft lithography of (most commonly) polydimethylsiloxane (PDMS), for example. U.S. Pat. No. 6,929,030 to Unger teaches a method of fabricating an elastomeric structure, comprising: forming a first elastomeric layer on top of a first micromachined mold, the first micromachined mold having a first raised protrusion which forms a first recess extending along a bottom surface of the first elastomeric layer; forming a second elastomeric layer on top of a second micromachined mold, the second micromachined mold having a second raised protrusion which forms a second recess extending along a bottom surface of the second elastomeric layer; bonding the bottom surface of the second elastomeric layer onto a top surface of the first elastomeric layer such that a control channel forms in the second recess between the first and second elastomeric layers; and positioning the first elastomeric layer on top of a planar substrate such that a flow channel forms in the first recess between the first elastomeric layer and the planar substrate. According to Unger, nearly any elastomeric polymer is suitable, but the only examples given are fabricated from silicone rubber, specifically GE RTV 615 (formulation), a vinyl-silane cross-linked (type) silicone elastomer.
Unger teaches two parallel layers having transversely oriented channels, one for control and the other for fluid flow. Movement of the membrane separating the control and fluid flow channels (due to the control channel being pressurized or the membrane being otherwise actuated) cuts off flow passing through the fluid flow channel.
Other references on this subject are: A. P. Sudarsan, J. Wang and V. M. Ugaz, “Thermoplastic elastomer gels: an advanced substrate for microfluidic device construction”, Analytical Chemistry, 77, 5167-5173, 2004; U.S. Pat. No. 6,408,878 to Unger et al.; US Patent Application publication number 2002/0168278 to Whitesides et al.; and U.S. Pat. No. 5,512,131 to Kumar et al. There are a wide range of useful high throughput testing facilities and microfluidic devices for feeding a solution to a variety of inputs, for sorting, mixing, filtering or selectively applying different treatments to one or more fluids to be analyzed, for crystallization, or for feeding optical (or other) interrogation instruments or reaction chambers. In many cases it is desirable to provide a limited volume of a reagent, cleaning solution, or other chemical species for selective reaction with a test sample, for example.
For example, U.S. Pat. No. 6,808,522 to Richards et al. teaches a method of producing a plurality of reservoirs in a hard silicon based chip for releasing the molecules stored therein. The method requires capping the reservoirs and release systems for the reservoirs for uncapping them when needed.
Applicant has filed a patent application Ser. No. 12/588,236 directed to the use of thermoplastic elastomers (TPEs) for use in microfluidic devices, TPEs having advantages over PDMS and other known materials in terms of bonding and patterning of layers for microfluidic devices.
There remains a need in the art for better systems for controlling flow within microfluidic devices, and in particular for providing a releasable reservoir.